Organizing BiodiversityDichotomous Keys

But what if we find things we

don't know and we want to

know what they are?

What’s my name !?

We use something’s

characteristics (called

their morphology) in a

similar way using…

Dichotomous Keys A dichotomous key is a tool that allows the

user to determine the identity of items in

the natural world based on the items

morphology

"Dichotomous" means

“divided into two parts” Greek origin

dichotomous keys always give two distinct

choices in each step, often they are opposites

Black/white; or pointed/rounded

How to use a dichotomous key?

HA! HA!Dichotomous Keys

Here are fictitious, diverse creatures we don’t know!

Before we start, what level of diversity is this?

Now, lets choose one

How to use a Dichotomous Key?

Choose only one creature at a time.

How to use a Dichotomous Key?

Read steps 1a and 1b

Decide which statement is true

How to use a Dichotomous Key?

1b is true

Then follow the directions after that step.

How to use a Dichotomous Key?

At choice 5, you make another dichotomous choice

How to use a Dichotomous Key?

5a is true

Keep going until you come to a step

that gives you the creature’s name.

How to use a Dichotomous Key?

6 a. The creature has one antennae Go to Step 7.

Choose a new creature and start at step 1a and 1b again. Continue until you find the creature’s name.

C

How to use a Dichotomous Key?

Where do you start Again?

Then, find the names of all the

creatures

1. a. wings covered by an exoskeleton – go to step 2

b. wings freely observed – Go to step 3

2. a. body has a round shape ……….ladybug, a red beetle with black spots

b. body has an elongated shape ……….grasshopper, a green insect that hops

3. a. wings point out from the side of the body ……….dragonfly, an insect that is 10- 15 cm long and lives in marshes

b. wings point to the posterior of the body ……….housefly, a flying insect with red eyes and an annoying buzz

What if I needed to make a key:- Use constant characteristics rather than variable ones.

(Flowers change with the seasons)

- Use measurements rather than terms like "large" and "small".

- Make the choice a positive one

- something "is" instead of "is not".

- Ex: snake ears are internal only

- If possible, start both choices of a pair with the same word or item.

- the body is “round” vs the body is “square”

- Finish the dichotomous key with a full description of the organism

Dichotomous key

1 With flower.

Without flower

Angiosperms

Go to 2

2 Seedless.

Seed bearing

Go to 3

Gymnosperms

3 Plant body do not differentiated into root,

stem and leaves.

Plant body differentiated into root, stem and

leaves

Go to 4

Go to 5

4 Without photosynthetic pigment.

With chlorophyll or other photosynthetic

pigment

Algae

Fungi

5 No vascular tissues.

With vascular tissues

Mosses

Fern

Another Example of a dichotomous key…

Dichotomous key

the dichotomous key can also be expressed in a diagram form

Non-flowering plants

Without photsyn-

thetic pigment

With chlorophyll or

other photosynthetic

pigment

Algae Fungi

No vascular

tissuesWith vascular

tissues

Mosses Gymnosperms

Plant body not

differentiated into

root, stem and

leaves

Plant body

differentiated

into stem and

leaves

Seedless Seed-bearing

Ferns

Flowering Plants

(Angiosperm)

Without flowerWith flower

Plants